Abstract

A search for dark matter particles is performed by looking for events with large transverse momentum imbalance and a recoiling Higgs boson decaying to either a pair of photons or a pair of τ leptons. The search is based on proton-proton collision data at a center-of-mass energy of 13 TeV collected at the CERN LHC in 2016 and corresponding to an integrated luminosity of 35.9 fb−1. No significant excess over the expected standard model background is observed. Upper limits at 95% confidence level are presented for the product of the production cross section and branching fraction in the context of two benchmark simplified models. For the Z′-two-Higgs-doublet model (where Z′ is a new massive boson mediator) with an intermediate heavy pseudoscalar particle of mass mA = 300 GeV and mDM = 100 GeV, the Z′ masses from 550 GeV to 1265 GeV are excluded. For a baryonic Z′ model, with mDM = 1 GeV, Z′ masses up to 615 GeV are excluded. Results are also presented for the spin-independent cross section for the dark matter-nucleon interaction as a function of the mass of the dark matter particle. This is the first search for dark matter particles produced in association with a Higgs boson decaying to two τ leptons.

Highlights

  • Background estimation and signal extractionA narrow resonance search similar to the SM Higgs boson diphoton analysis of ref. [51] is performed

  • The SM Higgs boson branching fractions to γγ and τ +τ − are smaller than the branching fraction to bb, the analysis presented here exploits these two decay channels because they have unique advantages compared with the h → bb channel

  • The background yields and the observed number of events within 3 GeV of the SM Higgs boson mass are listed in table 5 for both the low- and high-pmTiss categories

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Summary

The CMS detector and event reconstruction

The central feature of the CMS detector is a superconducting solenoid, of 6 m internal diameter, providing an axial magnetic field of 3.8 T along the beam direction. Using information from all CMS subdetectors, a global event reconstruction is performed using the particle-flow (PF) algorithm [21]. The PF algorithm optimally combines all of the detector information and generates a list of stable particles (PF candidates), namely photons, electrons, muons, and charged and neutral hadrons. Additional corrections, calculated from the mass distribution of Z → e+e− events, are applied to the measured energy scale of the photons in data (≤1%) and to the energy resolution in simulation (≤2%). Electron reconstruction requires the matching of the cluster of energy deposits in the ECAL with a track in the silicon tracker. The HPS algorithm uses combinations of reconstructed charged hadrons and energy deposits in the ECAL to reconstruct the τ lepton’s three most common hadronic decay modes: 1-prong, 1-prong + π0(s), and 3-prong. Event filters [29] are applied to remove such events

Observed and simulated data samples
Event selection
Background estimation and signal extraction
Signal extraction and background estimation
Systematic uncertainties
Observed yields
Interpretation in the Z -2HDM model
Baryonic Z model interpretation
Simplified DM model interpretation
Summary
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